Hereinafter in this description and in the subsequent claims the expression “vision system” indicates an apparatus that is able to acquire and possibly process images that is used in various applications such as, for example, automatic inspection for quality control, measurements without contact, selecting and positioning industrial pieces, reading and checking optical information, inspecting materials for detecting defects or dimensional checks, supervision, biometric recognition and access control, etc.
Hereinafter in this description and in the subsequent claims, the expression “optical information” indicates a graphic representation having the function of storing encoded or non-encoded information. A particular example of optical information consists of linear or two-dimensional optical codes, in which the information is coded through suitable combinations of elements with a preset shape, for example, square, rectangular, or hexagonal, with a dark colour (normally black) separated by light elements (spaces, normally white), such as barcodes, stacked codes and the bidimensional codes in general, colour codes, etc. The term “optical information” further comprises, more in general, also other graphic forms, including particular printed characters (letters, numbers, etc) and shapes (“patterns”) (such as, for example, stamps, logos, signatures, digital fingerprints etc). The term “optical information” comprises graphic representations that are detectable across the entire wavelength comprised between infrared and ultraviolet and therefore not only in the visible light field.
An example of a vision system that is able to acquire images associated with an object placed on a supporting plane (for example distance, volume, overall dimensions of the object, or data identifying the object, in particular an optical code associated with the object) by acquiring and processing an acquisition zone at the supporting plane.
The vision system is a system—in particular a fixed system—capable of capturing images of objects or people, of subjects in general, and in particular of optical information, by means of a plurality of possible acquisition techniques.
For example, acquisition can be performed by illuminating a subject, collecting with a suitable optical receiving system, for example comprising an objective, the light diffused by the subject on a sensor consisting of an array of light-sensitive elements of a linear or matrix type, for example of the CCD or CMOS type, and generating an image signal by means of an electronic system integrated or associated with the sensor. The image signal, generated in analogue or digital form, can then be processed in the same apparatus or in a separate image processing system.
Typically, in vision systems dedicated to the acquisition of images containing coded optical information, such as barcodes, the image signal in digital form is decoded to extract the information content of the code.
Apparatuses of this type are known as linear or matrix TV cameras or cameras, and when they read optical information, they are also known as code-reading devices of the “imager” type.
Hereinafter in this description and in the subsequent claims, the expression “fixed vision system” indicates a vision system the position of which with respect to the supporting plane is not varied during operation, for example a vision system for use without human operation (“unattended system”), in particular at a conveyor belt (or other moving means) on which objects to be detected are moved, but also at a station in which an operator inserts the objects to be detected manually. Detecting the objects may comprise reading an optical code and/or measuring a distance and/or a volume, etc.
A drawback of known vision systems is that they are rather complicated to install, in particular, dedicated operations are necessary to check and, possibly, to adjust the focussing thereof. In known vision systems fixed-focus and adjustable-focus systems are distinguished.
A further drawback of known vision systems is that an installer is unable to define visually when the system is focussed. Checking focussing, in fact, requires the vision systems—i.e. the detecting sensors with which the vision systems are provided—to be switched on to detect the image of a sample figure. If the detected image is not clear, it is necessary for the installer to intervene manually on the objective to adjust the focussing of the vision systems.
This checking method, comprising a plurality of consecutive refinements of focussing, involves the acquisition of a series of sample images, so actuation thereof takes a long time.
In addition, it necessary to provide a display, for example the monitor of a computer, to enable the installer to examine the detected images. In other words, installation of the known vision systems requires the provision of complex and expensive equipment.